What with all the noise, work was impossible. I wandered to my top-floor window and found myself eyeball to eyeball with a man dangling in a vast oak, swinging a chainsaw.

I love that oak. It stands on the street beside the garden of my neighbour’s house. To pass the time, I’ve sketched and painted it several times. Now it seemed it was about to be cut down.

It’s one of many: on the same day last week the London Assembly warned that the capital’s 7m trees are falling victim to a “chainsaw massacre” – some 40,000 full-grown trees have been cut down by London councils in five years.

According to the Greater London Authority, Barnet cut down 2,400 trees in the last five years – making mine the capital’s third most destructive borough after Croydon (2,600 trees sacrificed) and Harrow (an amazing 5,000).

We wring our hands over the depleted Amazon rainforest. Does nobody care about the steady deforestation of our towns and cities?

“Everyone thinks trees are a good thing,” says Graham Simmonds of Trees for Cities, an independent charity. “There’s a positive impact on global warming, they beautify the city, they are good for our health – and yet forces are conspiring against urban trees.”

The most significant force “conspiring” against urban trees is the fear of subsidence: 40% of the trees cut down are lost because thirsty trees dry out the kind of clay soil we have in London. There were £25m worth of claims against London boroughs in 2003, a drought year.

But Andy Tipping, chairman of the London Tree Officers Association, says many claims blaming trees for subsidence are questionable. He says Barnet has successfully resisted 90% of those claims, with the result that only 100 trees have been removed for that reason.

Other trees are removed for a variety of reasons: because they obscure the view for CCTV cameras, because pigeons nest among them and bespatter cars parked beneath, or because the falling leaves cause blockages. Someone in Barnet, Tipping says, demanded that a tree be cut down after a puppy nearly choked on acorns.

But the fact is that trees add value to cities. In leafy areas property prices are 18% higher than elsewhere, research shows, and crime rates and domestic violence are almost 50% lower.

A tree-lined street produces 90% less dust than a treeless one, and can be 10F cooler. Trees protect against floods and sunburn, suck up smog and chemicals, reduce noise and generate oxygen: a large beech produces enough for 10 people.

Many local councils argue that they are planting trees as fast as they fell them. But there’s no way that a tiny sapling can replace a mighty oak. Many new trees will never grow to a great size, because local authorities increasingly plant smaller, ornamental trees that are less “threatening” to houses.

I could not sit back and watch the tree being cut down. Marching round to the back of the house, I prepared to deliver a lecture about pollarding, which – when it’s done properly – prevents even large trees posing a danger to buildings.

Over the noise of his masticator, the tree-murderer couldn’t hear a word. But then he turned off the machine and mildly explained that this particular oak was staying, it just needed tidying up a bit. So at least one urban tree is safe – for now.

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